Add USX - Update feature-availability.md

Author: cwatson-cat

articles/sentinel/feature-availability.md

@@ -126,6 +126,12 @@ While Microsoft Sentinel is also available in the [Microsoft Defender portal](mi
 |[Workspace manager](workspace-manager.md) |Public preview | ✅ |✅ |❌ |
 |[SIEM migration experience](siem-migration.md) | GA | ✅ |❌ |❌ |
 
+## Microsoft unified security operations platform
+
+|Feature  |Feature stage |Azure commercial  |Azure Government |Azure China 21Vianet  |
+|---------|---------|---------|---------|---------|
+|[Microsoft Sentinel within the Microsoft unified security operations platform](/defender-xdr/microsoft-sentinel-onboard) |GA| ✅ |❌ |❌ |
+
 ## Normalization
 
 |Feature  |Feature stage |Azure commercial  |Azure Government |Azure China 21Vianet  |